Interconnect and Energy Efficiency: Towards Sustainable Technologies

A brief overview of global trends in renewables

Photovoltaic (PV), wind, and hydropower are the main sources of renewable energy in the US with biomass and geothermal following behind. In early 2023 electricity from coal and nuclear power fell below that of renewable energy sources within the US. Many countries already obtain the majority of energy produced from renewable sources including Iceland, Norway, Brazil, New Zealand, Colombia, and more. China and the US lead in installed renewable energy capacity where China produces over 2,500 GW from non-fossil power generation, meeting the 50% renewable energy target set for 2025 this year, in 2023.

Solar

This race towards decarbonization of the energy sector is fueled primarily by solar, wind, hydroelectric, and geothermal alternatives. Solar power has become more accessible with more affordable options and vendor diversity for PV panels, energy storage, and charge controllers/inverters. Solar panels are also growing in efficiency where most commercial panels have an efficiency between 17% to 20%. Researchers have developed solar cells with efficiencies going beyond 40%, and while these cells are not even close to being production ready, these values show that progress is continually being made in photovoltaics. Solar inverters are also increasing in efficiency through the use of wideband gap switching devices with silicon carbide (SiC) where the increase in switching speeds and high thermal conductivity of the substrate allows for lowered switching losses and simpler thermal management design. Energy storage systems (ESSs) such as batteries are also continually being developed for specific energy, energy density, cycle life, and calendar life, ultimately allowing for more battery capacity per unit area.

Wind and hydropower

Wind power is also seeing enhancements with larger rotor diameters and more installations cropping up both onshore and offshore to maximize the higher wind speeds found in bodies of water. Turbines are also growing taller, allowing for more power output per installation. As shown in Figure 1, the typical construction of a wind turbine includes the hub, rotor, nacelle, and tower. The nacelle usually houses the gearbox and generator where power generated is then converted and stepped-up via a transformer before it is distributed to the grid. The conversion of wind energy to electricity is optimized by controlling the pitch of the turbine blades as well as the yaw, or orientation, of the nacelle.

Hydropower installations contribute to a significant percentage of global renewable energy; this type of renewable power source uses the natural flow of moving water, for example, from a dam through a channel known as a penstock, to move a turbine and generator and create electricity (Figure 2).

Advancements in turbine efficiency continue to occur with improvements in turbine design. Advancements in tidal power—or hydropower that takes advantage of the water flowing from high tide to low tide with axial and cross-flow turbines—continues to occur. Other creative hydropower solutions such as smaller, modular hydropower designs and hydropower that utilizes wave energy are being researched and implemented to enhance renewable power capacity.

Connector considerations for sustainable technologies

Renewable energy installations must consider the strains of outdoor environments from water ingress from high humidity atmospheres, rain, snow, and hail, as well as the potential water immersion in solar and wind offshore plants. Dust exposure and ingress will often occur, this is especially the case in dry environments such as deserts. Solar farms are meant to be built in areas where sun exposure is high; however, UV radiation is a major contributor to the accelerated aging of materials used in electronics enclosures and connectors. Electronics should not come into contact with highly reactive materials such as salt or chemicals as this can very rapidly contaminate and destroy conductors through corrosion, this often referred to electrolytic corrosion (Figure 3). With these environmental strains multicontact ingress protection (IP) rated connectors. The IP rating system will classify the degree of dust and moisture protection by an enclosure for electrical equipment where an IP6x rating ensures the connector is entirely dust tight. An IPx7 or higher (e.g., IP67, IP69, etc.) will ensure the connector can withstand temporary immersions in water. Connectors with these ratings will generally be able to endure rain and high humidity environments.

Mechanical stresses can also occur from vibrations and constant flexure. This issue is often found in the long vertical cable runs found within towers, the shear wind forces cause the installation to vibrate. This, for example, is the case within cell towers. Wind turbine cables could be subjected to worse vibration due to their windy environment and the moving parts within the tower. Vibration is a factor that must always be considered within these wind-powered systems as failure mechanisms such as fretting corrosion can occur. In fretting corrosion, metal surfaces in contact with each other, such as connector pins, rub repeatedly causing wear such as pitting and material transfer from one surface to the other. Corrosion can occur on the newly exposed surface causing more surface roughness and scraping, eventually leading to a failure. Connector heads without the proper retention force can quickly un-mate when tugged on, causing disconnects with electronics within the nacelle such as the generator, converter, transformer, or programmable logic controller (PLC).

Commonly used connectors in renewables

All of these potential connector failure modes due to mechanical, electrical, and environmental strains can be mitigated through adequate ruggedization. Environmental strain is largely addressed with resistance to moisture and dust, this prevents any contaminants from entering the mate, ensuring the fidelity of a connection regardless of the environment (e.g., salty atmospheres, deserts, high humidity environments, etc.). Vibration tends to be the most severe mechanical duress a cable assembly will undergo, even more so than mechanical shock. Connectors with a high level of mating cycles, sufficient plating thickness, mates with a high retention strength, and connector pins that offer a high integrity connection, all lessen the impact that vibration will have on the connector housing. EDAC supports renewable energy systems with a selection of relevant connectors that have been ruggedized to withstand the various strains from these applications.

Connections in solar farms

IEC 62548, NEC, and UL6703 are all standards for PV system design that require PV connectors within an installation to be of the same type and brand to eliminate the risk of operator shock from cross-mating. So, ease of installation is quite clearly a deciding factor for PV connectors, especially since the average 100 MW farm can contain over 100,000 connectors [2]. Large solar farms often used MC4 connectors to string panels together and scale up power. EDAC also offers PV connectors that come with a protective cap to provide both water and dust protection. Other commonly used connectors occur between battery modules in a rack and between the racks themselves to ensure all energy is stored for usage. These rocks will often use RS485, RS232, or CAN serial communications for monitoring and control with either a D-subminiature (d-sub) or RJ45 ethernet connector. USB connectors can also be used with portable PV panels for USB charging on-the-go. Since this is generally for outdoor usage, connectors will need to be ruggedized against moisture and dust. EDAC offers waterproof d-sub and USB connectors that use a proprietary epoxy sealing process that seals the entire back of the connector rather than at individual pins and are fully tested to IP67 standards (Figure 4).

Connections in wind farms

The issue of connectors getting un-mated when tugged on in wind turbines is easily resolved by using connectors with some type of strain relief in tandem with a connection that cannot be reversed easily such as latches, threading, or bayonet-type locks on the connector head. Within wind turbines, compression terminal kits are often used to make vibration-proof splices when wiring. EDAC offers power connectors with insulation displacement connectors (IDC) and surface mount (SMT) terminations that could be a good fit in wind turbine installations.

Other connectors used within turbines include high-voltage connectors for the power conversion system, power and signal connectors for the control units within the nacelle or at the base of the tower, and wet mate connectors that can be submerged in water for subsea transformers in offshore wind farms. EDAC’s waterproof d-sub connector is ideal for use within these control units as these come with both power and signal connections, allowing for a singular space-saving and ruggedized connector solution. Inline connectors are a viable option for distributing signal connections with wire harnessing within the nacelle. These connectors are also waterproof and offer a double-latch technology that has been tested to be both vibration-resistant and have a high retention strength.

Ruggedized connections for renewables

Renewable energy farms and power plants are constantly being built globally to support the ever-increasing demand for electricity without relying on the diminishing resources of the past. These systems rely on their connectors in order to properly transfer large amounts of power to the grid, monitor and control equipment, and simply connect between subsystems to either scale up power or scale up energy storage. These connectors will be exposed to various strains that could cause them to fail prematurely. In order to avoid this, it is critical to integrate ruggedized connections that can withstand potential moisture, dust, and chemical ingress, as well as UV exposure and high mechanical strain from wind or poor cable handling.

References

1. [1]Liu, Xingyong; Ji, Xiangying; and Zhu, Dexiang, “Electrolytic Corrosion Resistant Plating for Connector Pins”, Technical Disclosure Commons, (August 04, 2020), https://www.tdcommons.org/dpubs_series/3493.
2. [2]“Evolving Challenges for PV Cables and Connectors.” UL, 14 Dec. 2022. Web.